Traditionally, a number of devices have been utilized to protect semiconductor devices from high voltages, such as those that occur during electrostatic discharge (ESD). For example, conventional thyristors have been utilized to protect semiconductor devices from high voltages that result from ESD. In general, the conventional thyristor is a four-layer or four-diffusion semiconductor device, with alternating N-type and P-type layers or diffusions, e.g., NPNP or PNPN. The main terminals (i.e., anode and cathode) of a thyristor are across all four layers or diffusions and a control terminal (i.e., gate) is attached to one of the middle layers or diffusions. The operation of a thyristor can generally be understood in terms of a pair of coupled transistors (i.e., an NPN transistor and a PNP transistor), arranged to cause a self-latching action.
One shortcoming of a conventional thyristor is that, like a diode, it only conducts in one direction. Another drawback associated with a conventional thyristor is that it is not a fully controllable switch, in the sense that the triggering current direction needs to be reversed to switch the thyristor off. Yet another shortcoming of a conventional thyristor is that it is not readily integrated with a semiconductor device that is to be protected.
What is needed is a protection device that can be readily integrated with a semiconductor device that is to be protected from electrostatic discharge.